Index: src/OFZIPArchive.m
==================================================================
--- src/OFZIPArchive.m
+++ src/OFZIPArchive.m
@@ -117,11 +117,11 @@
 
 	return field;
 }
 
 static uint32_t
-crc32(uint32_t crc, uint8_t *bytes, size_t length)
+calculateCRC32(uint32_t crc, uint8_t *bytes, size_t length)
 {
 	size_t i;
 
 	for (i = 0; i < length; i++) {
 		uint_fast8_t j;
@@ -132,10 +132,25 @@
 			crc = (crc >> 1) ^ (CRC32_MAGIC & (~(crc & 1) + 1));
 	}
 
 	return crc;
 }
+
+static void
+seekOrThrowInvalidFormat(OFSeekableStream *stream,
+    of_offset_t offset, int whence)
+{
+	@try {
+		[stream seekToOffset: offset
+			      whence: whence];
+	} @catch (OFSeekFailedException *e) {
+		if ([e errNo] == EINVAL)
+			@throw [OFInvalidFormatException exception];
+
+		@throw e;
+	}
+}
 
 @implementation OFZIPArchive
 + (instancetype)archiveWithSeekableStream: (OFSeekableStream*)stream
 {
 	return [[[self alloc] initWithSeekableStream: stream] autorelease];
@@ -203,19 +218,11 @@
 	uint16_t commentLength;
 	of_offset_t offset = -22;
 	bool valid = false;
 
 	do {
-		@try {
-			[_stream seekToOffset: offset
-				       whence: SEEK_END];
-		} @catch (OFSeekFailedException *e) {
-			if ([e errNo] == EINVAL)
-				@throw [OFInvalidFormatException exception];
-
-			@throw e;
-		}
+		seekOrThrowInvalidFormat(_stream, offset, SEEK_END);
 
 		if ([_stream readLittleEndianInt32] == 0x06054B50) {
 			valid = true;
 			break;
 		}
@@ -242,12 +249,11 @@
 	    _centralDirectoryEntries == 0xFFFF ||
 	    _centralDirectorySize == 0xFFFFFFFF ||
 	    _centralDirectoryOffset == 0xFFFFFFFF) {
 		uint64_t offset64, size;
 
-		[_stream seekToOffset: offset - 20
-			       whence: SEEK_END];
+		seekOrThrowInvalidFormat(_stream, offset - 20, SEEK_END);
 
 		if ([_stream readLittleEndianInt32] != 0x07064B50) {
 			objc_autoreleasePoolPop(pool);
 			return;
 		}
@@ -260,12 +266,12 @@
 		offset64 = [_stream readLittleEndianInt64];
 
 		if ((of_offset_t)offset64 != offset64)
 			@throw [OFOutOfRangeException exception];
 
-		[_stream seekToOffset: (of_offset_t)offset64
-			       whence: SEEK_SET];
+		seekOrThrowInvalidFormat(_stream,
+		    (of_offset_t)offset64, SEEK_SET);
 
 		if ([_stream readLittleEndianInt32] != 0x06064B50)
 			@throw [OFInvalidFormatException exception];
 
 		size = [_stream readLittleEndianInt64];
@@ -299,12 +305,12 @@
 	size_t i;
 
 	if ((of_offset_t)_centralDirectoryOffset != _centralDirectoryOffset)
 		@throw [OFOutOfRangeException exception];
 
-	[_stream seekToOffset: (of_offset_t)_centralDirectoryOffset
-		       whence: SEEK_SET];
+	seekOrThrowInvalidFormat(_stream,
+	    (of_offset_t)_centralDirectoryOffset, SEEK_SET);
 
 	_entries = [[OFMutableArray alloc] init];
 	_pathToEntryMap = [[OFMutableDictionary alloc] init];
 
 	for (i = 0; i < _centralDirectoryEntries; i++) {
@@ -353,12 +359,11 @@
 
 	offset64 = [entry OF_localFileHeaderOffset];
 	if ((of_offset_t)offset64 != offset64)
 		@throw [OFOutOfRangeException exception];
 
-	[_stream seekToOffset: (of_offset_t)offset64
-		       whence: SEEK_SET];
+	seekOrThrowInvalidFormat(_stream, (of_offset_t)offset64, SEEK_SET);
 	localFileHeader = [[[OFZIPArchive_LocalFileHeader alloc]
 	    initWithStream: _stream] autorelease];
 
 	if (![localFileHeader matchesEntry: entry])
 		@throw [OFInvalidFormatException exception];
@@ -566,15 +571,15 @@
 		ret = [_decompressedStream readIntoBuffer: buffer
 						   length: min];
 		_size -= ret;
 	}
 
-	_CRC32 = crc32(_CRC32, buffer, ret);
+	_CRC32 = calculateCRC32(_CRC32, buffer, ret);
 
 	return ret;
 }
 
 - (void)close
 {
 	_closed = true;
 }
 @end